Automatic transmission fluids (ATFs) present highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating and power transmitting requirements of modern automatic transmissions (including continuously variable transmissions of various types). Many additive components are typically included in an ATF, providing such performance characteristics as lubrication, dispersancy, friction control (for clutches), antiwear performance, anti-shudder performance, anti-corrosion and anti-oxidation performance. Finding and providing the correctly balanced composition is a significant formulating challenge. Furthermore.
Examples of formulations that have been employed in the past include those represented by U.S. Pat. No. 5,164,103, Papay, Nov. 17, 1992, which discloses preconditioned ATFs made by using a preblend formed by heating an alkenyl succinimide or succinimide detergent with a phosphorus ester and water to partially hydrolyze the ester, and then mixing the preblend and other additives with a base oil. Boronating agents may also be used. Thiadiazole derivatives may be included as another additive.
U.S. Pat. No. 5,344,579, Ohtani et al, Sep. 6, 1994, discloses a friction modifier composition which may be used in a wet clutch or wet brake system. The composition comprises a hydroxyalkyl aliphatic imidazoline and a di(hydroxyalkyl)aliphatic tertiary amine. The compositions may also contain a phosphorus-containing ashless dispersant and/or a boron-containing ashless dispersant. Among other components are copper corrosion inhibitors such as 2,5-dimercapto-3,4,-thiadiazole.
U.S. Pat. No. 6,251,840, Ward, Jr. et al., Jun. 26, 2001, discloses an automatic transmission fluid comprising a majority of an oil having a certain viscosity, 0.025-5 weight percent 2,5-dimercapto-1,3,4-thiadiazole (DMTD) or one or more derivatives of DMTD, an antifoam agent, and 0.01-0.3 weight percent of 85% phosphoric acid. Derivatives of DMTD include products from combining an oil soluble dispersant with DMTD. These may be obtained by mixing a thiadiazole, preferably DMTD with an oil-soluble carboxylic dispersant in a diluent by heating the mixture above about 100° C.
U.S. Pat. No. 4,136,043, Davis, Jan. 23, 1979, discloses compositions which form homogeneous blends with lubricating oils and the like, produced by preparing a mixture of an oil-soluble dispersant and a dimercaptothiadiazole and heating the mixture above about 100° C. The compositions are useful for suppression of copper activity and “lead paint” deposition in lubricants.
U.S. Patent Application 2003/0224948, Van Dam et al., published Dec. 4, 2003, discloses an additive formulation containing ethylene carbonate polyalkene succinimides, borated dispersants and dispersed aromatic dicarboxylic acid corrosion inhibitors that are succinimide salts of one or more aromatic dicarboxylic acids.
The present invention solves the problem of providing a lubricating composition, especially for an ATF capable of providing at least one property from acceptable friction performance and durability, acceptable anti-shudder performance, acceptable oxidation resistance and acceptable gear protection.